In the completion of oil and gas wells, the practice is to drill a well bore from the earth's surface, insert a tubular steel casing in the well bore and fill the annulus between the casing and well bore with a cement slurry which sets and supports the casing in the well bore. Thereafter, a deeper section of well bore is drilled with a smaller diameter than the diameter of the surface casing. The drilling bit is removed from the deeper section of the well bores and a liner, (which is a string of connected lengths of tubular, steel pipe joints) is lowered through the surface casing and into the open section of the well bore. The liner at its upper end is attached to a liner hanger which is releasably attached to a setting tool on the lower end of a string of drill pipe. The drill pipe supports the weight of the liner on the setting tool as the setting tool and liner are lowered into the well bore. The length of the liner is predetermined so as to have its lower end proximate to the bottom of the open well bore with its upper end section and an attached liner hanger overlapping the lower end of the section of casing above. The setting tool is operated to set slips on the liner hanger against and in gripping engagement with the casing so that the liner is "hung" or suspended in the open well bore by the slips in the lower end of a casing or pipe. With a hydraulically operated setting tool, the slips are set by dropping a check valve ball into the string of drill pipe so that the ball or plug is pumped or falls into a ball valve seat to close off the bore of the pipe at a location below the setting tool. Next, by building up hydraulic pressure in the drill pipe, the slips are set by the hydraulically operated mechanism in the setting tool. Thereafter, by increasing the pressure in the drill pipe, the ball valve seat is released to provide an open condition in the pipe below the setting tool so that cement slurry can be pumped through the liner for cementing an annulus.
Usually, the setting tool is released from the liner hanger prior to cementing. After the setting tool is released from the liner hanger, the exterior of the open pipe on the setting tool remains sealed off with respect to the bore of the liner so that a cement slurry can be pumped down the drill pipe through the open pipe and through the liner. At the lower end of the liner is a cementing shoe and back pressure valves (sometimes called cementing float equipment) and the slurry of cement is displaced by surface pumping equipment to flow through the cementing shoe and into the annulus between the liner and the open well bore. The cement slurry is displaced upwardly until the volume of cement in the annulus is at a desired level which is generally a level overlapping the top of the liner above. During this operation there is mud or control fluid in the well bore and mud or control fluid driving the cement slurry. Thus, when the cement slurry is introduced through the drill pipe it is generally followed by a cementing plug which wipes the internal surface of the drill pipe as it is moved through the drill pipe to minimize contaminating the cement slurry with mud or control fluid and to wipe the drill pipe. When the cementing plug reaches the setting tool it latches into a liner cement wiper plug (which is usually typically larger in diameter than the I.D. of the drill pipe) and the liner cement wiper plug and coupled cementing plug then follow the cement slurry. The liner cement wiper plug wipes the I.D. of the liner. The liner cement wiper plug stops when it bumps a landing collar or float equipment in the liner.
As noted above, in the setting operation for the liner hanger with a hydraulic setting tool, it is possible to drop a ball which seats in a ball valve seat at a valve seat location below a hydraulic actuating means in the setting tool. The valve seat location is usually in a specially constructed sub attached in the lower end of the liner just above the float equipment. In this type of valve seat, continued applied pressure shifts the seat to reopen the liner bore for cementing. The sub and valve are not retrieved and thus are consumable or expendable to the operation.
If a ball valve seat is located in the setting tool, release of the ball valve seat and ball is through the end of the setting tool pipe, and the attached wiper plug. In this case, the ball valve seat is not retrieved and becomes debris in the well bore and there is a risk of prematurely dislodging the wiper plug from the setting tool.
When the ball valve seat is located in a sub at the lower end of a liner, it is necessary to pressure up the entire liner to set a hydraulic setting tool. In any case, the ball valve seat assembly is an expensive consumable item and not reusable.
In another practice, a liner hanger and liner are lowered to the desired location and the liner is hung in a casing as above described with a valve seat in the setting tool. After the liner is hung, the setting tool and attached drill pipe are removed from the well bore prior to the cementing operation. Next, drill pipe with a polished mandrel at its lower end is lowered into the liner until the polished mandrel enters and seals with respect to a sealing bore located at the lower end of the liner. Typically, the sealing bore is part of the float collar or the float shoe. With this arrangement then, cement slurry can be pumped directly through a drill pipe and through the cementing equipment at the lower end of the liner neither contacting the internal bore of the liner nor imposing any pressure to the bore of the liner. However, as can be appreciated, this system requires two trips of a drill pipe, i.e., a first trip of drill pipe with a setting tool to hang the liner and a second trip of drill pipe with a polished surface mandrel to utilize the drill pipe in a sealed bore at the lower end of the liner.
In a co-pending application, S/N 147,533, filed Jan. 25, 1988, and assigned to the assignee of the present invention, a method and apparatus is disclosed in which a liner is made up at the earth's surface in an appropriate length for a well bore. At the lower end of the liner is an internal sealing bore located just above the cement floating equipment. The liner when made up to the desired length and disposed in the well, is initially hung in casing slips at the earth's surface while a drill pipe is connected up joint by joint at the earth's surface and lowered into and through the liner. At the lower end of the drill pipe is a section of polished mandrel which is sized for sliding and sealing engagement within the internal sealing bore in the liner. Also disposed in a section of pipe at the lower end of the drill pipe is a lower ball check valve for operating a hydraulic setting tool and an upper cementing plug valve for opening a bypass in the drill pipe upon completion of the cementing injection. The drill pipe is made up in sections until the polished mandrel is stabbed or inserted into the sealing bore at which time a hydraulic setting tool and liner hanger are attached to the drill pipe and to the liner respectively so that the setting tool can support the liner hanger, the liner and the internal string of drill pipe within the liner. The surface casing slips are then released and a running-in string of drill pipe is made up by connecting drill pipe joints and the entire assembly of drill pipe and liner is lowered into the well bore to the desired location depth. At the desired location depth a trip ball or plug for the check valve is dropped and pumped through the drill pipe to seat in the lowermost ball check valve in the drill pipe so that a hydraulic pressure buildup can occur in the drill pipe for actuating the hydraulic setting mechanism in the setting tool. The setting tool then brings the slips of the liner hanger into setting engagement with the inner wall of the next above casing or pipe.
When the setting tool is actuated and the slips on the liner hanger are set, an increase or pressure buildup in the drill pipe causes the lower check valve to open a port and the valve is retained in the drill pipe while the lower end of the drill pipe is opened to the port. The setting tool is then disconnected from the liner hanger by release of a threaded nut coupling so that the supporting drill pipe is not connected to the liner hanger during the cementing operation and the polished mandrel at the lower end of the string of drill pipe remains in sealing relationship to the sealing bore in the liner. Thereafter, cement can be pumped down the drill pipe from the earth's surface through a drill pipe of substantially uniform internal diameter and the calculated volume of cement slurry can be followed by a cement wiper plug in the well-known manner. When the cement wiper plug engages the upper bypass valve in the liner, the bypass valve is opened so that the interior of the liner and the interior of the drill pipe are in fluid communication after the cementing operation is complete thereby relieving the drill pipe from retrieving any fluid when the drill pipe is removed. In this system it is necessary to pressure up the entire length of drill pipe which extends to the float equipment.
In any system, however, a particular problem arises when the end of the liner with a valve seat is located in a non-vertical location such as a deviated or horizontal section of well bore. In such instances it is extremely difficult and sometimes not possible to obtain seating of a ball or closure member in a small, centrally located valve seat opening at the lower end of a liner. Often if there is any question regarding operability under such conditions the equipment will not be used.
Some components which are utilized in the present invention have been used in a type P-1 landing sub available from TIW in Houston, Tex. The P-1 landing sub has a ball valve seat releasably coupled to a collar by a resilient ring. The resiliently expansible ring is normally held in a contracted position by a pressure responsive piston. When pressure is applied, the ring is released from the holding effect of the piston but is held in position by applied pressure on the ball valve. When the applied pressure is reduced on the ball valve, the ring unsnaps from or expands to release the ball valve seat so it can fall out of the collar.
Collet type valve seats have also been used in the past where the ball seats on relatively short upwardly directed collet fingers so that the collet fingers are under compression when the ball is seated on the fingers. A shear pin release permits a shift of the fingers to a location where the collet fingers are expanded to release the ball member. The collet fingers must be short and stubby to prevent crushing under compressive forces. Thus, the fingers have little resiliency and do not expand greatly and for a full opening, a large diameter ball is required. A large diameter ball raises the possibility of prematurely actuating a wiper plug when released. Also the pump down plug for the wiper plug must be larger than the ball diameter.